1. Field of the Invention
The invention is generally related to welding of two cylinders together and more particularly to the clamping, aligning, rounding and welding of large diameter cylinders together.
2. General Background
Various methods exist to align and clamp two cylinders for welding. Several methods use multiple shoes to apply force to the inside diameter of each of the cylinders to be welded. Details of some of these methods are as follows.
Shoes consisting of arc segments are machined to match the inner diameter of the cylinders to be welded. These arc segments are welded together to create a U-shaped channel, creating a back purge chamber between the two clamping segments. The arc segments are manually positioned and then held in place by a spoked arrangement. Force is applied to the segments by tightening nuts which run on threaded rods in the spokes. Gaps between the segments and the cylinders must be caulked (e.g. silicon (RTV) in order to prevent the back purge gas from leaking out. This equipment is very time consuming to install, is not very accurate, and the risk of damaging the component is high.
A wheel hub is positioned inside the cylinders. Multiple shoes are inserted between the hub and the cylinder. In between the shoes and the hub is a fire hose, which is then pressurized with air to provide the necessary force to clamp and round the cylinders. Since shoe position is dependent on uniform inflation of the fire hose, alignment of the shoes is not very accurate. This method does not provide a closed chamber for back purging.
Rather than use in a curved shoe against the cylinder, another method uses a series of swivel-headed bolts to push on the inner diameter of the cylinder. The bolts are anchored into an arc segment, which is moved into rough position by motor driven screw jacks. After the arc segments are positioned close to the cylinder inner diameter, each of the bolts is manually adjusted to provide the proper force on the inner diameter of the cylinder. This method is very time consuming and does not provide accurate fit-up since the cylinder can flex in the area between the push bolts.
Some other methods do not employ shoes of any kind. For example, struts can be fabricated from pipe or tubing material, and forced into the inner diameter of the cylinder. This method is best suited to heavy walled cylinders that readily retain their own shape and for applications where a high degree of accuracy is not required.
Another method is to use consumable inner diameter rings which are machined to provide an interference fit with the inner diameter of the cylinders. The rings are shrunk into the inner diameter of the cylinders, and provide internal rounding pressure as they expand. The rings would then be cut apart to remove them from the cylinder.
The inventors are not aware of an existing tool design that satisfies al of the following design requirements for making circumferential welds in large diameter cylinders. Because fit-up of the cylinders is critical to control both weld quality and to meet final dimensional requirements for the cylinder assemblies the tool must permit almost perfect alignment of the cylinders to be joined and allow the cylinders to be anchored on location to maintain alignment during rolling and welding. To correct cylinder out-of-roundness within 0.010 inch, mismatch must be essentially eliminated in order to achieve proper fit-up. The tool must provide sufficient in/out stroke length to provide clearance with cylinder inner diameter features at the small diameter (retracted position) and long enough to effectively apply force to the inner diameter of the cylinders. Clamping force should be selectable and displayed for the operator. Tooling located near the welding arc must be fabricated from non-magnetic materials in order to prevent disturbance of the welding arc (known as "arc blow"). The material must also be able to withstand the heat from the welding operation. It must be possible to create a sealed back purge chamber to be flooded with an inert gas to prevent oxidation of the backside of the weld. An electrical grounding path must be provided for the welding arc. The tooling must be symmetrical and balanced for proper rotation during welding. The design must allow proper installation, use, and removal without scratching or marring the final machined cylinder surfaces.